This invention relates generally to the field of seating for aircraft, busses and trains, where multiple rows of seats are used and more particularly to a seat back frame for absorbing energy.
Passengers are generally seated in a forward facing fashion in aircraft, busses and trains. Most seats are arranged in rows of seats installed one row behind the other throughout the cabin. Most passengers face a seat back frame positioned directly in front. A safety hazard results from the typical restraint system utilized on the seats. Such restraint system usually include only a traditional lap belt and do not include an upper torso restraint such as a shoulder restraint. In the event of a high G forward crash, the head of the seat occupant is not restrained and is free to accelerate forward and violently strike the seat back frame located in front of the occupant.
At the time of a forward crash, a person's head strikes the seat back frame of a seat in the rows of seats located in front. It is obvious, however, that this impact cannot be avoided. Thus, any method to reduce the impact by absorbing or dissipating the energy is considered important.
In addition to absorbing impact energy, seats should be structurally strong, reliable and capable of positioning a passenger for comfort and safety for the duration of the trip. Under normal operating conditions, the entire seat configuration is subject to various loads and external forces, such as the weight and movement of an occupying passenger, or contact from others behind or near the seat.
A variety of seats designed to absorb and dissipate head impact energy exist in the prior art. Initially, seat backs were modified to absorb impact energy by padding the rear side of the seat back with materials such as a sponge rubber, semi-hard urethane foam, or pad materials such as cotton to the rear side of the seat back. To provide adequate protection, the thickness of the padding material substantially reduces the space available for passengers, and the seats become overly bulky.
A seat assembly described in U.S. Pat. No. 3,537,751 (Inoue et al.) provides for a somewhat less space consuming seat assembly. In the Inoue et al. patent, the seat has a seat back with a shock absorbing shell member. The shell member has a C-shaped cross section and is secured on a seat back frame in such a manner that a hollow shell space is placed in the direction in which the seat back is subject to a possible impact. The shell space withstands normal loads imposed on the seat back, and collapses when the seat back frame is subject to extreme loads such as impact resulting from a vehicle collision. Although the Inoue et al. patent allows the seat assembly to occupy less space, it is still preferable to have a back seat which is relatively thin to comfortably seat a maximum number of passengers in a vehicle.
The need to provide seat assemblies which are relatively light weight and require a relatively small of amount of space has been somewhat addressed by adding mechanical devices to the seat frame assembly to absorb and reduce the head impact load. Government agencies have established limits for the acceptable head injury criteria, i.e. HIC. Various approaches are presently utilized to absorb and dissipate the head impact energy. Most of the approaches are mechanical and require the deforming of materials or use of friction devices to function. One of the disadvantages of such approaches is that they do not perform adequately in crash condition involving multiple impacts.
For example, U.S. Pat. No. 5,676,421 (Brodsky) includes a seat with a plurality of shear pins which sequentially dissipate energy over a period of time. The energy absorption mechanism provides adjustable shear force and energy absorption based upon varying seat back angles. The shear pins sequentially shear to dissipate energy over time. However, the shear pins are unable to dissipate energy from subsequent impacts once they have been sheared.
U.S. Pat. No. 4,349,167 (Reily) describes an aircraft passenger seat having a plurality of integrally mounted wire-bending energy attenuators. Once deformed, the attenuators may not be adequately absorb the energy from subsequent impacts.
U.S. Pat. No. 5,344,210 (Marwa) describes an aircraft seat assembly having an elongated one piece element pivotally connected to front and rear seat supporting legs. The one piece element is crescent shaped with two curved arm portions of opposite convexities separated by a space arranged in a central portion of the crescent shape. During an impact, the one piece element is permanently deformed and may not be able to absorb energy from subsequent impacts.
U.S. Pat. No. 5,344,210 (Sharon) describes an aircraft seat movable between a first unloaded and a second crash induced position. During a crash induced movement of the seat, a deformable rod is pulled through a reducing die where the diameter of the rod is reduced, and the impact energy is absorbed as the rod is deformed. Since the rod is permanently deformed, the ability to absorb energy from subsequent impacts may be substantially reduced.
U.S. Pat. No. 5,320,308 (Bilezikjian et al.) describes an airline passenger seat having a shear pin which acts as a guide for the forward tilt rotation of a seat back. Integral with the seat back is a channel structure including restraining slots of a fixed length. The channel structure pivots about an arm member, and the slots "travel" along the shear pin. Under normal operation, once the seat back has rotated forward to a limited "forward tilt" position, the slots have traveled their full length and stop against the respective shear pins, which prevent further forward motion of the seat back. In the event of an excessive force acting on the seat back, such as impact from a passenger behind the seat back in a severe crash, the load is translated to the shear pins and the shear pins break off. The seat back rotates freely beyond the parameters defined by the slots, until restrained by the seat structure itself, a passenger therein, or the seat back in front of it. In addition, the fitting assembly includes a friction brake or clutch arrangement to inhibit tilting of the set back at all times but does not prevent the complete forward rotation of the seat back. The "brake-force" load needed to tilt the seat back is substantially less than the force required to shear the shear pins. Thus, once the shear pins break, the seat back is still capable of being placed in its fixed, non-tilting upright position. However, the passenger seats are unable to absorb energy from subsequent impacts because the shear pins are permanently sheared.
U.S. Pat. No. 5,340,059 (Kanigowski) describes an energy absorbing cabinet assembly attached to a rear wall of an aircraft cabin bulkhead and positioned directly in front of passengers sitting in front-row seats. The cabinet assembly includes a storage box unit with an airline-type foldable food table. Both the cabinet support structure and food table structure are made from energy absorbing materials and are capable of yielding and deforming under an impact from behind to protect the heads of front-row passengers during crash landing emergencies. However, the cabinet assembly is unsuited for protecting non front-row passengers seated behind seats.
Thus, there remains a need for an improved seat assembly which is capable of absorbing energy resulting from multiple crash impacts. In addition, there remains a need for a seat back which is relatively resistant to forces directed in the aft direction and yet relatively flexible to forwardly directed forces. Generally, seat comfort is substantially improved when the seat back is relatively rigid to support the passenger while sitting and reclining. Furthermore, there remains a need to provide an energy absorbing device which is relatively inexpensive and light weight.